Display devices are increasing in importance due to the wide-spread use of mobile devices, such as cell phones. There are numerous types of displays including Organic Light-emitting Diode (OLED) displays, Light-emitting Diode (LED) displays and Liquid Crystal Displays (LCD). The displays are used in a wide-range of applications, including consumer devices such as cell phones, gaming devices, watches, etc. The OLEDs use thin-film transistors in a backplane that switch pixels on or off so as to generate images on the display. LCDs, by contrast, typically use a backlight in conjunction with light-modulating properties of liquid crystals. Often the displays include multiple layers of glass. For example, an OLED display assembly can include a cover glass (also called a “window”), an encapsulation glass, and a Low-Temperature Polycrystalline Silicon (LTPS) glass.
In the manufacture of displays, frit is often used as an intermediate material in binding pieces of glass together. The frit is a ceramic composition that, when heated, melts to hermetically bind the glass pieces. The frit is often melted with a laser that is passed over the frit near the edges of the display. While the laser melts the frit, it can also damage any signal traces that overlap the frit, such as touch traces. Pressure sensors can also be located in the area of the frit and can, likewise, be damaged by the laser as it melts the frit. In addition, the pressure sensors are a conductive (metal) layer and can block the laser from the frit. As such, the unmelted frit will not adequately bind the pieces of glass together. For this reason, the pressure sensor pads are limited to a display area where they do not interfere with the laser.
Regardless of location, any capacitance-based pressure sensors often require an air gap below a display substrate so that a distance between a reference ground and a sensing pad can be changed. The air gap adds to the integrated height of the display and restricts how thin a final device can be manufactured.
Therefore, there exists ample opportunity for improvement in technologies related to pressure sensors.